Tongue is the mirror of your health. It may reflect certain problems in your body that is why doctors often check up your tongue. Tongue: your health monitor. Here is an article on how to examine your own tongue. But as i always say, you can not fully count on that.
1. Hairy tongue: when the small bumps which are normally on everyone tongue become larger, they make your tongue appear hairy. This case is harmless, however if it is bothering you, you will need to take anti-biotics.
2. Geographic tongue: condition is characterized by smooth, bright red patches on the top of the tongue. The patches can change size and location from day to day (and have a map-like, or geographic, appearance). A completely harmless condition, the geographic tongue is not a case that bothers you.
3. Red tongue: More serious case. If your tongue is red, you are suffering deficiencies of vitamins. Consult your doctor.
4. Pale tongue: Nutritional deficiencies, B-12 deficiency, or anemia.
5. Black tongue: Caused by bacteria that accumulates on your mouth. This is often a harmless condition.
6. White tongue: Caused by smoking, drinking, alcohol.
Note: some stomach problems may cause white appearance on your tongue, even if you do not smoke. Also, white tongue can be a Candida sign. Candida is painful most of the time. I have one thing left to say, many changes occur in the tongue which are harmless. You do not need to panic, but if you feel pain, or something that bothers you, or conflicts in eating, or speaking, you need to consult a doctor as those symptoms usually mean a more serious disease.